In a cellular communication network, a geographic area served by the network is divided into a number of cell sites, each defined by a radio frequency (RF) radiation pattern from a respective base transceiver station (BTS) antenna. The BTS antennae in the cells are in turn coupled to a base station controller (BSC), which is then coupled to a telecommunications switch or other gateway, thereby facilitating communication with a telecommunications network such as the PSTN (public switched telephone network) or the Internet.
When a mobile station (such as a cellular telephone, personal digital assistant, or appropriately equipped portable computer, for instance) is positioned in a cell, the mobile station communicates via an RF air interface with the BTS antenna of the cell. Consequently, a communication path is established between the mobile station and the telecommunications network, via the air interface, the BTS, and the switch or gateway.
With the explosive growth in demand for wireless communications, network resources can be stressed. For instance, as the level of call traffic increases in a typical cell site, the likelihood of interference between mobile stations can increase substantially. In response to such an increase in call traffic, the base station of the cell may instruct all mobile stations in the cell to decrease their transmission power, and the base station may itself begin to communicate at a lower power level with each mobile station in the cell. With lower transmission power, however, call quality can diminish, and calls may ultimately be lost.
Further, changes to topography such as new building or growth or removal of trees can substantially effect the operation of a wireless network. For instance, as buildings and trees rise or fall in or around a cell site, the radiation pattern of the cell site may change drastically. As a result of new or changed signal reflections, for instance, the signal-to-noise ratio in or around the cell site may become unacceptably low and calls may be dropped.
To help manage the call traffic in congested or evolving areas and in other circumstances, a cellular telephony service provider may make changes to the network, such as by repositioning cell sites, subdividing cell sites into a number of sectors, adding new cell sites, or reallocating frequencies among various coverage areas. However, in order to effectively decide when and where such changes should be made, and to otherwise provide subscribers with acceptable and expected quality of service, a need has arisen to monitor the performance of the cellular network infrastructure.
One way to monitor cellular resources is to send technicians out into the field (i.e., into cell sites) with mobile diagnostic measurement (MDM) tools, to collect diagnostic data about network conditions. MDM tools are known and commercially available from companies such as ZK Celltest, Xcellon, Ericsson, and Agilent. Once the data is collected, the data can be analyzed (typically with a computer on the cellular provider network), and determinations can then be made about the state of the network and about what changes if any may be required.
Conveniently, the MDM tool may be carried in a vehicle such as a car, so that measurements can be made at various geographic locations. In one scenario, one technician drives the vehicle around town, while another technician in the vehicle operates the MDM tool so as to record information about the network. Alternatively, the MDM tool can simply be carried in the vehicle and can automatically collect information about the network.
Ideally, the MDM tool would further include a GPS receiver adapted to collect location data points indicative of where the MDM tool made its measurements. The MDM tool establishes a log file that includes records, each indicating measured network conditions and a corresponding geographic location. Further, the log file can include an MDM identifier that identifies the MDM tool that collected the data.
In most current MDM products, the MDM tool wirelessly transmits the log files to a central computer or server, via an RF transmitter in the MDM tool and a wireless packet data connection (e.g., via FTP) to a node in the wireless network. An analyst reviewing the data then makes decisions about allocation of system resources.
The process of driving or otherwise conveying an MDM tool around a given geographic area to collect network information is known as “drive testing.” Conveniently, with the advent of automated MDM tools, a wireless carrier can arrange with a trucking company, taxicab company, public transportation company, or other carrier to mount MDM tools in various vehicles so as to collect network information from throughout a desired area as those vehicles drive along their routes, which are referred to as “drive test routes.”
In its simplest configuration, a MDM tool includes (i) a first measurement device (e.g., mobile phone) that collects performance metrics (e.g., air interface condition data etc.), (ii) a computer coupled with the first measurement device for receiving the collected performance metrics and compiling them, and (iii) a transmitter (e.g., a second mobile phone) coupled to the computer, for receiving the collected performance metrics from the computer and transmitting them via an air interface and radio access node connection to a server. At the server, the data is compiled, reported, and analyzed, e.g., to facilitate making improvements to the network.
In typical practice, MDM tools (drive test units) are more complex than this, however. The MDM tool may take the form of a chassis that couples together (i) a wireless modem card for wirelessly reporting collected performance metrics, (ii) a CPU/controller, and (iii) up to n test phones, where n is some integer greater than 1, such as 5 or 10. The controller can control the various phones to cause them to do various things (such as placing calls, interacting with location-determination systems, engaging in signaling messaging, etc.), and the controller can collect information about the actions and results/responses/conditions with respect to those test phones. All of that logged data can be compiled into one file, with portions of the file corresponding to various ones of the test phones in particular slots of the chassis. Alternatively, separate files could be generated for the various test phones.
Background prior art references disclosing the state of the art in analysis of cell coverage in wireless networks and strategies for drive test routes include the following patents, each of which is incorporated by reference herein: Sanders et al., U.S. Pat. No. 6,754,487; Arpee et al., U.S. Pat. No. 6,711,404; Somoza, U.S. Pat. No. 6,336,035; Arpee et al., U.S. Pat. No. 6,606,494; Bernadin et al., U.S. Pat. No. 6,006,095; Rappaport et al., U.S. Pat. No. 5,451,839; Gutowski, U.S. Patent Application Publication US 2002/0063656; and Jensen, U.S. Patent Application publication US 2002/0009992.